1. Field of the Invention
The present invention relates to a lens device, which moves a lens in an optical axial direction, and an image pickup device and an optical device incorporating the lens device.
2. Description Related to the Prior Art
In recent years, digital cameras have become smaller in size. Along with this trend, lens devices incorporated in the digital cameras also have become miniaturized. Those digital cameras incorporated in compact electronic devices, such as cellular phones or PDA (Personal Digital Assistant), are especially made so small that their lenses are formed to have a diameter of a few millimeters. For those lens devices, pan focus (fixed focus) lenses are mainly used. However, those lens devices are required to have an auto focus function or a zooming function.
The lens device having the zooming function is constituted of, for instance, a zoom lens system consisting of front and rear lens groups, a first lens holder for holding the front lens group, a second lens holder, which is located behind the first lens holder, for holding the rear lens group, and a mount for housing these first and second lens holders movably, and is driven by a stepping motor. U.S. Pat. No. 6,744,156 discloses such stepping motor. The stepping motor comprises a stator for creating a magnetic field and a rotor, which is provided rotatably inside the stator. The stepping motor rotates the rotor in accordance with a driving pulse. Then rotation power of the rotor is transmitted to the first and second lens holders through a gear wheel, thereby performing the zooming of the zoom lens system.
It is also proposed to use a hollow-shaft stepping motor, which has a lens holder incorporated inside the rotor. In this case, a rotary barrel is mounted inside the rotor, and the rotor and the lens holder are connected through a helicoid mechanism. For this configuration, the lens device is driven without using the gear wheel.
However, the conventional devices have a problem being large in dimension since two stepping motors are used for driving the first and second lens holders individually.